If a true value, request a read-write version of this mailbox. If a
false value, request a read-only version.
(type: bool
)

Returns

The mailbox object, or a Deferred whose callback will be
invoked with the mailbox object. None may be returned if the specified
mailbox may not be selected for any reason.
(type: Any object implementing IMailbox or
Deferred
)

A true value if the given mailbox is currently subscribed to, a false
value otherwise. A Deferred may also be returned whose
callback will be invoked with one of these values.
(type: Deferred or bool
)